What is "collar day"

Collar \Col"lar\, n. [OE. coler, coller, OF. colier, F. collier, necklace, collar, fr. OF. col neck, F. cou, fr. L. collum; akin to AS. heals, G. & Goth. hals. Cf. Hals, n.]

1. Something worn round the neck, whether for use, ornament, restraint, or identification; as, the collar of a coat; a lady's collar; the collar of a dog.

2. (Arch.)

   1. A ring or cincture.

   2. A collar beam.

3. (Bot.) The neck or line of junction between the root of a plant and its stem.
   --Gray.

4. An ornament worn round the neck by knights, having on it devices to designate their rank or order.

5. (Zo["o]l.)

   1. A ringlike part of a mollusk in connection with esophagus.

   2. A colored ring round the neck of a bird or mammal.

6. (Mech.) A ring or round flange upon, surrounding, or against an object, and used for restraining motion within given limits, or for holding something to its place, or for hiding an opening around an object; as, a collar on a shaft, used to prevent endwise motion of the shaft; a collar surrounding a stovepipe at the place where it enters a wall. The flanges of a piston and the gland of a stuffing box are sometimes called collars.

7. (Naut.) An eye formed in the bight or bend of a shroud or stay to go over the masthead; also, a rope to which certain parts of rigging, as dead-eyes, are secured.

8. (Mining) A curb, or a horizontal timbering, around the mouth of a shaft.
   --Raymond.

   Collar beam (Arch.), a horizontal piece of timber connecting and tying together two opposite rafters; -- also, called simply collar.

   Collar of brawn, the quantity of brawn bound up in one parcel. [Eng.]
   --Johnson.

   Collar day, a day of great ceremony at the English court, when persons, who are dignitaries of honorary orders, wear the collars of those orders.

   To slip the collar, to get free; to disentangle one's self from difficulty, labor, or engagement.
   --Spenser.

Collar days are designated days on which the collar forming part of the insignia of certain members of British orders of knighthood may be worn. Collars are special large and elaborate ceremonial metal chains worn over the shoulders, hanging equally over the front and back, often tied with a bow at the shoulders, with a distinctive pendant attached to the front.